1. Field of the Invention
The present invention relates to a data backup system in a terminal device connected to a data communications network and, more particularly, to a data backup system for backing up individual information necessary for restarting each terminal device after recovery from its failure.
2. Description of the Related Art
In a data communications network, when a terminal device develops a fault, restoration of the fault is conducted by resetting the terminal device to initialize the same. In this case, data not retained in the terminal device at the time when the device is reset will be lost. Information necessary for the terminal device should be therefore obtained from another terminal device holding the lost data. Even if the failure occurring at a terminal device is a temporary failure such as failure resulted from runaway of a program caused by noise, or even if it is an easily recoverable failure, the same recovering procedure as that necessary for the above-described fatal failure is required. As a result, operation rate of the terminal device is lowered.
Concerning the above-described problem, for an easily recoverable failure occurring at a terminal device, there have been conventionally proposed various means for resetting the device and then automatically obtaining necessary information to recover from the failure. One of related art of this kind is recited, for example, in Japanese Patent-Laying Open (Kokai) No. Heisei 3-250835, entitled "Terminal Device".
According to the technique recited in the above literature, a terminal device connected to a center device via an ISDN line network includes, as shown in FIG. 3, a monitoring means 110 for detecting a failure occurring at each unit having an intelligent circuit such as a line interface unit, a line control unit and a device control unit, a resetting means 120 for resetting each of the above-mentioned units having an intelligent circuit when the monitoring means detects a failure, an initializing means 130 for initializing each unit which is reset, and a failure developing factor maintaining means 140 for maintaining a failure developing factor without being reset when the terminal device goes down. At each terminal device, when the monitoring means 110 detects a failure, the failure developing factor maintaining means 140 saves the failure developing factor and then the resetting means 120 resets every unit except the failure developing factor maintaining means 140. Then, after the self-diagnoses of a memory and an interface, each unit is initialized by the initializing means 130 to notify the center device of the maintained failure developing factor and boot the device.
According to the above-described conventional failure recovering technique, however, with a great failure, resetting the terminal device for the purpose of restoration results in erasing a failure developing factor maintained in the failure developing factor maintaining means 140, a parameter defining the operation state, various kinds of event information generated during the operation of the device and even variable information inherent to the terminal device. Restoration of the device to the state before resetting therefore needs labor and time, causing reduction in the operation rate of the system.
Another possible solution for efficiently obtaining necessary information at the time of restoration after resetting is to provide one master terminal device as a center device and concentratedly store information of all the terminal devices in a storage device provided in the master terminal device for the purpose of backing up data. This solution, however, has a drawback that it is impossible to back up the information of all the terminal devices when the master terminal device develops a fault.